Vulcanization of rubber



Patented July 21, 1942 v UNITED S'E'S VULCANIZATION F RUBBER New York NoDrawing. Application November 15, 1940, Serial No. 365,786

10 Claims.

This invention relates to the vulcanization of rubber and to rubbercompositions vulcanized in the presence of the accelerators hereindescribed.

It has long been known that the time required for vulcanization ofrubber can be greatly reduced by the employment of materials commonlyknown as accelerators. We have discovered the thiazolinyl disulfides tobe exceedingly efiicient accelerators for rubber vulcanization.

This class of compounds has never before been used for the accelerationof rubber vulcanization, largely because of the recorded inactivity ofthe 2-mercapto thiazolines from which they are derived. Sincemercaptobenzothiazole, an excellent accelerator, is more active than itscorresponding disulfide, the same relationship would be expected betweenthe mercaptothiazolines and the corresponding disulfides. However, Wehave found that, contrary to expectations, the thiazolinyl disulfidesare considerably more active than the mercapto thiazolines from whichthey are derived.

The accelerators of our invention may be prepared by oxidation of thecorresponding mercapto thiazoline by means of a suitable oxidizing agentsuch as sodium hypochlorite, sodium persuliate, sodium nitrite, nitricacid, hydrogen peroxide, sodium perchlorate, etc., as follows:

where R is hydrogen, or an alkyl, aryl, or alkoxy group. Two of the Rgroups on adjacent carbon atoms may be joined to form a reduced cyclicgroup containing three or more carbon atoms. Mercapto thiazolines whichyield suitable disulfides include such compounds as 2- mercaptothiazoline; Z-mercapto l-methyl thiazoline; 2-mercapto 4-phenylthiazoline; Z-mercapto 5-ethyl thiazoline; Z-mercapto l-methoxymethylthiazoline; 2-mercapto 4,5-dimethyl thiazoline; 2-meroapto 4,5-diethylthiazoline; 2- mercapto l-p-aminophenyl thiazoline; 2-mercapto4.,5-tetramethylene thiazoline; and the like.

We have also found that materials which activate mercapto thiazoline,such as monocarboxylic acids and their metallic salts, as disclosed inour copending application Serial No. 255,358,

filed February 8, 1939, also serve as activators for our newaccelerators.

The acid used to activate the accelerator may be any monocarboxylicacid, saturated or unsaturated, such as lauric, stearic, caprylic,oleic, linoleic, palmitic, benzoic, salicylic, or the like; or the saltsof these acids with metals such as zinc, lead, tin, sodium, calcium,magnesium, or any other alkali, alkaline earth, or heavy metals may beused. It is preferred to use the higher fatty acids, but the lower acidsmay be used, preferably in the form of the metal salts. Beneficialeffects are obtained by using very small amounts of the acids or theirsalts; however, the best results are achieved by the presence of 1 to 5%or more of these activators.

As evidence of the effectiveness of our new accelerators the followingcompositions were prepared:

A B O D Rubber 100. 0 100. 0 100.0 100. 0

3. 5 3. 5 3. 5 3. 5 Zinc oxide 5.0 5.0 5.0 5.0 Laurie acid 0.0 3.0 0.03.0 Dithiazolinyl dlsulfi 1. 0 1.0 0. 0 0.0 Bis(5-methyl thiazolinyl)disu1fide 0.0 0.0 1.0 1.0

After curing in a mold at 237 F., the compositions above had thefollowing properties, where T=tensile strength in pounds per square inchand E=elongation in per cent: a

From these results it is apparent that although the activating el'fectof the acid is appreciable, nevertheless good cures and good tensilestrengths are obtained even in the absence of the activator.

These new accelerators are effective not only with natural rubber orcaoutchouc, but also with balata, gutta-percha, latex, rubber isomers,or any synthetic rubber which can be vulcanized, that is, which losesits property of thermoplasticity and becomes elastic, when heated in thepresence of sulfur, and the term a rubber is used in the claims todesignate all of the abovementioned materials. Pigments, fillers,reinforcing agents, softeners, antioxidants, other accelerators, etc.may be present in the rubber composition.

The accelerators of our invention are not limited to any particularcompositions, but may be used for pneumatic or solid tires, footwear,hose, tubes, surgical goods, belting, dipped articles, and all manner ofrubber goods.

The method of vulcanization used is not limited to that disclosed in thespecific examples, but includes heating the rubber composition withsteam, hot air, hot water, etc.

Although we have herein disclosed specific examples of our invention, wedo not intend to limit ourselves solely thereto, for many modi ficationsand variations lie within the spirit and scope or the invention asdefined in the appended claims.

We claim:

1. The process of vulcanizing a rubber in the presence of dithiazolinyldisulfide and a number of the class consisting of monocarboxylic acidsand their metallic salts.

2. The process of vulcanizing a rubber in the presence of bis(5-methylthiazolinyl) disulfide and a member of the class consisting ofmonocarboxylic acids and their metallic salts.

3. The process of Vulcanizing a rubber in the presence of dithiazolinyldisulfide and lauric acid.

4. The process of vulcanizing a rubber in the" presence of bis(5-methylthiazolinyl) disulfide and lauric acid.

5. A composition comprising a. rubber vulcanized in the presence ofdithiazolinyl disulfide and of a member of the class consisting ofmonocarboxylic acids and their metallic salts.

6. A composition comprising a rubber vulcanized in the presence ofbis(5-methyl thiazolinyl) disulfide and of a member of the classconsisting of monocarboxylic acids and their metallic salts.

7. A composition comprising a rubber vulcanized in the presence ofdithiazolinyl disulfide and lauric acid.

8. A composition comprising a rubber vulcanized in the presence ofbis(5-methyl thiazolinyl) disulfide and lauric acid.

9. The process of vulcanizing-a rubber in the presence of a thiazolinyldisulfide containing no substituent groups other than alkyl, alkylene,alkoxy, and aryl groups, and of a member of the class consisting ofmonocarboxylic acids and their metallic salts.

10. A composition comprising a rubber vulcanized in the presence of athiazolinyl disulfide containing no substituent groups other than alkyl,alkylene, alkoxy, and aryl groups, and of a member of the classconsisting of monocarboxylic acids and their metallic salts.

PAUL c. Jones. M ROGER A. MATHES.

